I went out with my bf for 11 and a half months. I did not have a day when I didn't speak to him or see him. Then two weeks before our year anniversary, he two timed with a mate of mine.
I thought I was going crazy. I was gettin really ill from all the pain he put me through. He then went out with one of my best mates. Now that hurt.
What I did was:
1) Didn't text him, ring him or try to contact him.
2) For three weeks, I didn't see or hear from him. It hurt but it was worth it.
3)Everyday after those 3 weeks, I realised that the separation had made things so much easier. And I could look at myself in the mirror and say that I, myself had got over something that I thought was impossible.

I suggest talkin to your mates, or someone who's gone through it. They will help you immensly and you'll realise you're not alone.
STAY STRONG. Remember, he's just a guy.